Master-Slave Strong Arm Latch for Wide Common-Mode Range
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Solution Overview
Problem
Strong Arm Latch (SAL) designs face limitations in common mode range, particularly at low power supply voltages, leading to large random offsets and limited applicability in applications requiring higher common mode ranges, resulting in increased power consumption and complexity.
Innovation Solution
The proposed solution involves a master-slave SAL topology with a differential input stage that complements both master and slave stages concurrently, allowing for a rail-rail input common mode range and reducing device stacking, along with a sampling and shift process that adjusts the common mode by discharging sampling capacitors during the evaluation phase, ensuring operation at low Vcc with minimal power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If traditional SAL topology is used, then device complexity is reduced, but input common mode range is limited within Vcc supply
Solution Approach 1:
The patent divides the SAL into master and slave stages, each handling different portions of the common mode range. The master SAL handles lower common mode voltages while the slave SAL handles higher common mode voltages, allowing the overall system to achieve a common mode range exceeding the supply voltage without requiring excessive device stacking in a single stage.
Solution Approach 2:
The patent extends the common mode range beyond the traditional single-supply constraint by operating the master and slave SALs in different voltage domains. By using different supply voltages (Vcc1 for master, Vcc2 for slave) and different threshold voltages, the system achieves operation in a second dimension of voltage range.
2Adaptability or versatility
If P-SAL and N-SAL are used together to expand common mode range, then adaptability improves, but device complexity and dead zone increase
Solution Approach 1:
The patent uses dynamic switching between master and slave SALs based on the input common mode voltage level. The switching is controlled by comparing the common mode voltage against threshold levels, automatically enabling the appropriate SAL (master or slave) without requiring complex control logic. This dynamic operation eliminates the dead zone by ensuring continuous coverage as the common mode voltage transitions between ranges.
3Use of energy by moving object
If aggressive power scaling is applied, then power consumption reduces, but headroom of SAL operating region narrows
Solution Approach 1:
The patent changes the supply voltage parameters used by different SAL stages to optimize the trade-off between power consumption and operating headroom. The master SAL operates at a lower supply voltage (Vcc1) to reduce power consumption, while the slave SAL operates at a higher supply voltage (Vcc2) to provide sufficient headroom when needed, achieving both low power operation and adequate operating range.
Data Source
AI summary
Described is an apparatus to widen or improve a common mode range of a strong arm latch (SAL). In some embodiments, the SAL comprises a master-slave architecture with a common latch. The apparatus includes: a sampler to sample an input with a first clock, and to provide a sampled output on a node. The SAL is to receive the sampled output on the node, and to sample the sampled output according to a second clock. The apparatus comprises a digital-to-analog converter (DAC) coupled to the node, wherein the DAC is to adjust a common mode of the sampled output according to a digital control to the DAC.